Summary of Work: NIAMS has an ongoing protocol to study polymyositis. As part of this protocol, subjects are imaged with magnetic resonance imaging (MRI) using a special pulse sequence that suppresses signal from fat but enhances signal from diseased tissue. In the past, the images were usually evaluated visually to determine the extent and the progress of disease. A more quantitative method for analysis has been developed and is being tested. This method produces a three-dimensional histogram of signal intensity values. In normal subjects this histogram is nearly gaussian in shape, while in abnormal subjects this histogram is skewed to higher intensity values. A method was developed which is hoped will give quantitative indices of both the degree of disease as well as the volume of diseased tissue. This method is based on the assumption that the low signal intensity values within the tissue being studied represent normal tissue. The left half of the histogram is then reflected at about its peak to give an estimate of what the subject's histogram would have looked like if it were completely normal. Comparing the reflected histogram to the actual histogram allows estimates of the degree and volume of disease. The method is now completed and has been presented orally at the Society of Magnetic Resonance imaging. A manuscript describing the methodology has been submitted and is in review. The collaborating institute has begun using the method to evaluate subjects with polymyositis.